As a result of expected stricter legislation concerning the levels of nitrogen oxides (NOx) in exhaust gases from various types of internal combustion engines, extensive development is currently being carried out throughout the world to produce a system for the cleaning of exhaust gases and the reduction of the NOx levels. Many solutions have been proposed, many of which provide some level of improvement over previously known systems and methods, particularly when used in conjunction with relatively simple engine configurations.
However, the situation with respect to exhaust gas cleaning technology is much more complex where turbocharged engines (such as turbocharged diesel engines) with heavy operating conditions are concerned. Furthermore, these engines have a different operating cycle with higher loads during certification. Several solutions have been suggested, including expensive catalysis processes including several subprocesses (for example, injection of water, addition of urea) that in addition involve disadvantages in the form of complex and space-demanding components. The EGR (exhaust gas recirculation) concept, which has long been applied for lighter diesel engines in passenger cars, has attracted interest since it not only has advantages from the point of view of expense but also is expected to offer safe functioning and simple and compact construction, among other benefits.
During the turbocharging of heavy diesel engines that takes place when in operation, the pressure of the exhaust gases in most cases lies under the inlet pressure, and exhaust gases can therefore not be recirculated without measures being taken for achieving a supply of exhaust gases, in the form of, for example, venturi solutions, exhaust throttles or inlet throttles. However, these solutions have up until now been associated with disadvantages in the form of, for example, reduced engine power through high pressure losses, together with increased fuel consumption and smoke development.
By placing a venturi in the inlet flow, an advantageous difference in pressure between the exhaust and the inlet channel is achieved, and exhaust gases, which are removed upstream of the turbo, can be fed into the inlet pipe of the engine. A reduced NOx level is obtained as a result of the resulting lower combustion temperature.
U.S. Pat. No. 5,333,456 (Carter) discloses a flow valve in the shape of a coil that is placed upstream in the EGR supply flow. This control valve, however, can not be used in the inlet channels of turbocharged engines, as a result of its design and other considerations.
U.S. Pat. No. 5,611,204 (Cummins) discloses a flow regulator with venturi function, placed, however, in the inlet channel adjacent to the EGR supply flow. The opening for supply of exhaust gases is not located where the throttling of fresh air is greatest, which would involve a more severe throttling than necessary, while the total pressure losses, which arise from, for example, the neighboring actuating means, become significant.
The publication SAE 2000 World Congress, SAE Technical Paper Series 2000-01-0225 discloses a variable venturi with axial EGR supply. The design does not display a proper venturi shape since the fresh air is exposed to a momentary increase in area at the end of the injector pipe, and the pressure losses that follow from this design. The component must be equipped with an elbow, with its associated pressure losses, as a result of the axial supply, and furthermore, the fact that the dimensions of the component are unnecessarily bulky must also be considered. The arrangement is primarily intended for measurement purposes and has no interest with respect to normal operating conditions.
The disadvantages of the above-described prior art systems have been obviated by U.S. patent application Ser. No. 10/363,350, parent to the present application, in which is disclosed a flow regulator for EGR systems in the form of a variable venturi intended for mounting in the inlet part of turbocharged engines. The flow regulator includes a pipe section with a radial EGR supply flow and an essentially freely suspended body therein. The body can be displaced in the direction of the flow and is preferably designed such that the instantaneous throttling of fresh air is always greatest in the immediate vicinity of the inlet for supply of exhaust gases, independently of the position of the body. The throttling varies optimally during the regulation as a consequence of the variation with respect to the flow area of fresh air between the body and the wall of the pipe during supply of exhaust gases. In this way, the varying requirement for pumping is satisfied, with a minimum of pressure losses.
According to U.S. patent application Ser. No. 10/363,350, the venturi effect is principally achieved through the design of the streamlined body, and can in particular cases, be supplemented with a fixed venturi part, the diameter of which is either greater than or less than the greatest diameter of the drop section. An outlet cone (diffuser) can be incorporated with the rear part of the pipe section, as necessary, which makes its mounting possible in inlet channels with varying dimensions. According to one preferred embodiment, the body is controlled by an actuating means that is integrated with the body or that is arranged outside of the pipeline and connected to a front portion of the body. The first flow is not disturbed by such an actuating means, nor are any pressure losses caused. Furthermore, such a design can be produced considerably robust, compact, and displaying minimal external dimensions. The properties of the body, its location in the inlet channel and the actuating means allow a minimal disturbance of the supply of air to be achieved, and very good regulation is achieved with thorough mixing of the air supply for varying loads on the engine.
While the flow regulator disclosed in U.S. patent application Ser. No. 10/363,350 provides excellent results, and can be used in engines having a myriad of configurations, it has been discovered that in particular situations and in connection with engine systems having certain configurations, modifications to the flow regulator may be desirable. For example, the use of intercoolers in turbocharged engines has become common, which intercoolers are often large and consume a significant amount of space within the engine cavity. As such, space may become a concern. Moreover, the output port on the intercooler (or some other component to which the flow regulator is to be attached) and the input port on the engine manifold may be positioned such that a bend (of ninety degrees or some other angle) in the outlet conduit between the flow regulator and the engine manifold may be required. The Applicants of the present invention have discovered that such situations provide the opportunity for a beneficial modification of the flow regulator disclosed in U.S. patent application Ser. No. 10/363,350.
What is desired, therefore, is a system for mixing a first and a second gas flow which optimizes the mixing efficiency of the two flows, which minimizes pressure losses when mixing the two flows, which can be used in connection with turbocharged engines, which is compact in design and can be used in applications where space is of concern, and which is particularly adapted for use in applications where a bend in the outlet conduit is necessary or desirable.